They are also called 'impact printers'. The print head contains a grid of pins and different combinations of pins are pushed out to form different characters. The print head then hits a carbon ribbon leaving an imprint on the paper. This makes them fairly noisy as you can hear the pins striking the paper.

Dot-matrix printers are ideal when you need carbon copies. This is because the print head hits the paper with enough force that when carbonised paper is used, the impact makes a copy on the second sheet.

They are also useful when continuous paper needs to be used for example printing large quantities of invoices or bills. They can be printed onto paper with perforations and then separated by tearing once the printing is complete. 

Advantages

• Relatively cheap to buy
• Low operating costs
• Can print on continuous stationary
• Create carbon copies using carbonated paper
• Robust and will work perfectly well in harsh or dirty conditions such as garages or factories.

Disadvantages

• Print quality is poor and important documents are not suitable to give to managers or customers
• Very slow - slowest out of all three printers
• Noisy - you wouldn't want one of these printing all day in the office
• Cannot produce colour copies